[CONFIGURATION] Implement declarative configuration (config.yaml)

[marcalff]

Fixes #2481

Start with examples/configuration/main.cc

Changes

Please provide a brief description of the changes here.

• Declarative configuration is now available in opentelemetry-cpp
• Document this in the CHANGELOG

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.00%. Comparing base (0249b02) to head (a9bb682).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2518      +/-   ##
==========================================
- Coverage   90.01%   90.00%   -0.01%     
==========================================
  Files         225      225              
  Lines        7105     7105              
==========================================
- Hits         6395     6394       -1     
- Misses        710      711       +1     

see 1 file with indirect coverage changes

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[dbarker]

Great addition to the project!

[marcalff]

Great addition to the project!

Thanks.

According to github history for this PR, it took 273 commits to finally add 9 lines ;-)